The field of the invention pertains to thruster systems, including more particularly, screens for marine thrusters.
Marine vehicles, from large ships to umbilically controlled underwater robots (ROV""s) and small submarines, typically use ducted propeller thrusters to control their position and attitude and, except for large ships and some submarines, to provide main propulsion. These thrusters can experience problems not limited to thrust-limiting cavitation at and near the surface, interruption of operations from ingestion of foreign objects, creating hazards to marine life and divers, and excessive screen resistance to flow. These problems were addressed by a screen system described in the U.S. Pat. No. 6,152,793, titled SCREEN SYSTEM FOR MARINE THRUSTERS, which is incorporated fully herein by reference. However, the forward speed of a vehicle is still limited by the exit jet velocity of the thruster. A higher exit jet velocity would increase the thrust with the forward speed of a vehicle. Therefore, there is a need for a screen system that reduces thrust-limiting cavitation, while increasing the exit jet velocity of a thruster.
The present invention comprises screen having at least one opening and one constrictor associated with at least one opening. The constrictor changes the exit jet cross-sectional area to increase exit jet velocity, enhancing the overall thruster performance of propulsion devices.
The screens may be placed around propulsion devices in land vehicles, sky vehicles, and marine vehicles, such as those for ROV""s and small submarines, to assist positioning, attitude and overall propulsion. The screens, when made in larger dimensional scales, can be applied to large ship transverse thrusters at each end of the tunnel with the same advantages.